Cassegrain Lens

This all-metal reflecting optics lens was originally designed as a long
working distance, in-vacuum, on-axis lens yielding sub-micron diameter spot
sizes for laser microprobe mass analysers. The Cassegrain design has zero
chromatic aberration, so that any wavelength can be focused or viewed through
the lens. The lens is constructed by polishing the reflective surfaces directly
onto stainless-steel, which is normally then coated with aluminium and magnesium
chloride to enhance ultra-violet reflection. However, alternative coatings for
other wavelengths can be applied upon request. The all-metal construction means
high power laser intensities can be used and also allows the structure to be
baked for outgassing in an ultra-high vacuum environment.